This application requests continuation of the Iowa Cochlear Implant Clinical Research Center. Hearing preservation and combining acoustic plus electric speech processing have become very important concepts and our Center has played an important role in identifying the significance of residual acoustic hearing. We believe that hearing-preservation electrodes will improve outcomes because they allow users to combine electric auditory stimulation with any residual natural acoustic hearing. Our overarching goal is to examine how this hybrid approach to speech processing might benefit new populations of adults and children. We will also investigate the use of these less invasive electrodes in profoundly deaf infants, where they might help preserve the structural elements of the organ of Corti and enable this population to take advantage of ongoing future research to regenerate the peripheral auditory system. Our first objective aims to compare how electrode length affects the patient's ability to adapt to hearing the severely distorted frequency-place maps produced when acoustic plus electric stimulation are combined. This assessment will examine outcomes for hearing, speech and language, and music perception and enjoyment, and will also characterize Cl users in terms of underlying processing mechanisms. Thus, we propose to study the plasticity, learning, and adaptation mechanisms that might be central to predicting good outcomes. Our second objective is to define the boundaries between the appropriateness of hearing aids versus cochlear implants in populations of hard of hearing children. Third, we will examine whether profoundly deaf infants develop speech perception and language equally well with standard-length cochlear implants versus less invasive electrodes. We will study hearing-preservation electrode CIs in 105 adults and 80 children with residual acoustic hearing and 20 profoundly deaf infants. Control subjects will be obtained from a research registry that now has enrolled 335 previously implanted adults and children. Five research projects, an administrative Core A, and Patient Care, Speech Processing, and Technical Core B will address the above goals. The five research projects are highly integrated and depend on data from each other to answer the experimental questions.